1. Field of the Invention
This invention relates to an optical apparatus including a camera body and an interchangeable lens, etc..
2. Description of the Related Art
It has recently come to be practiced to arrange an LSI within an interchangeable lens of a camera system to permit power supply to the lens and communication between the lens and a camera body. Information pertaining to the lens is thus supplied to the camera body and an actuator disposed within the lens is controlled from within the camera body. In this instance, electrical connections between the lens and camera body are effected through groups of connecting contacts. Generally, one of the contact groups is arranged to be movable in the direction of contact while the other group is arranged to be stationary. On the side of the movable connection contact group, pin-shaped contacts are carried by a support member in such a way as to be movable in the contacting direction. The electrical connections are attained jointly by the groups of patterns provided on contact substrates and individual coiled springs made of a conductive material.
FIG. 5 of the accompanying drawings shows the conventional arrangement of a group of patterns 24a provided on a contact substrate 24. Each pattern 24a is formed in a size suited for contact with one of the coiled springs 23. The conventional patterns shown in FIG. 5 are evenly spaced at a pitch C. Therefore, the width of the whole pattern group 24a increases accordingly as the number of connection contacts increases. Meanwhile, it is a recent trend to have a greater number of connection contacts. As a result, a total angle occupied by these patterns 24a is approaching to 90 degrees as shown in FIG. 5. However, in mounting the interchangeable lens on the camera body, the increased angle necessitates the lens to be rotated relative to the camera body to a greater angle. Besides, the sliding distance of the connection contacts increases accordingly. The increased sliding distance then results in increased wear.
Further, U.S. Pat. No. 4,448,509 discloses a camera system, wherein among the group of contacts which include power-supply and grounding contacts which are related to the power supply, only the power-supply contact is disposed away from other contacts.
FIG. 6 shows the essential parts of a camera body to which the invention under the present application is related (not a prior art). Referring to FIG. 6, group of connection contacts and a group of patterns 24a which are arranged to be brought into electrical contact with the contact group by means of conductive coiled springs are formed on a contact substrate 24. FIG. 6 shows the contact substrate 24 as viewed from the reverse side (from the rear in the direction of an optical axis). Therefore, the patterns 24a are depicted with broken lines. The contact substrate 24 is secured with screws 25 to a substrate holder 21. The substrate holder 21 is in turn secured with screws 26 to a structural member 18 of the camera body.
The connection contacts of the camera body are disposed round the optical axis in the peripheral part of an area which is arranged to transmit a light flux coming from an object to be photographed. Therefore, the contact substrate 24 also extends round the optical axis. The substrate holder 21 also extends round the optical axis in such a way as to have the contact substrate 24 superposed thereon.
In the case of FIG. 6, the substrate holder 21 is screwed to structural member 18 of the camera body in a position to protrude from the contact substrate 24 in the direction around the optical axis. This has presented a problem that the length of a flange-back cannot be shortened. In other words, the area around the optical axis having the connection contact group is arranged to cause the flange-back to be affected by the thickness of the structural member 18 of the camera body. In order that the substrate holder 21 is firmly fixed, the mounting screws 26 must have a sufficient length in the structural member 18. Hence, it has been difficult to shorten the flange-back. It is another problem that the contact substrate 24 might be warped by the urging forces of the coiled springs. In other words, the connection contact group of the camera body is carried by the substrate holder 21 in such a way as to be movable in the direction of the optical axis. Under this condition, each contact of the contact group is electrically connected by each coiled spring to a corresponding pattern of the pattern group. The resilient force of the coiled springs, which increases when the connection contact group is pushed by coming into contact with the connection contact group disposed on the side of an accessory such as an interchangeable lens, is applied to the contact substrate 24. Then, since the contact substrate 24 is fixedly secured to the substrate holder 21, the strong resilient force acts to warp the contact substrate 24 and the substrate holder 21 on the screws 26. In FIG. 6, a reference symbol l.sub.3 denotes a distance between each of the screws 26 and a coiled spring located farthest from the screw 26. The above-stated warping force acts substantially more strongly as this distance l.sub.3 increases. The warp may be prevented by increasing the strength of the substrate holder 21 by increasing its thickness. However, such a method is not desirable in respect of cost and the flange-back.
Further, with regard to the camera system of the above-stated kind, U.S. Pat. No. 4,999,659 issued Mar. 12, 1991 and U.S. Pat. No. 5,021,872 issued Jun. 4, 1991, have proposed a method of reducing the contact resistance of connection terminals which are related to the power supply among the electrical connection terminals of the camera body and the accessory by arranging these power-supply related terminals to have a greater contact pressure between them than contact pressure between other terminals. According to the method, the coiled springs themselves are arranged to serve as electrical conduction paths. In cases where contact resistance is to be set at such a small value that is less than 0.1 ohm, this arrangement hardly meets the requirement, because each of the coiled springs has an electrical resistance value much greater than 0.1 ohm.